Method and device for the autocombustion of oily organic waste,comprising a tangential heating furnace

ABSTRACT

The present invention relates to a method and to a device intended for spontaneous combustion of a fuel comprising organic, vegetable or mineral materials, the device comprising a combustion chamber, at least one fuel injection means, at least one air inlet, hot fumes discharge means. Chamber ( 1 ) comprises a cylindrical shell ( 11 ), the discharge means comprise a pipe ( 6 ) having the same axis as the chamber and arranged inside said chamber, and fuel injection means ( 7 ) is arranged substantially tangential to said cylindrical shell so that the fuel follows a circular motion around said pipe in the chamber.

FIELD OF THE INVENTION

The present invention relates to the field of combustion and notably ofspontaneous combustion of organic and preferably greasy waste.

A particularly interesting application of the invention relates to theuse of the combustion energy in a heat exchanger such as a hot waterproduction device.

BACKGROUND OF THE INVENTION

French patent application FR-2,774,454 describes a water heating devicecomprising a firing chamber with a primary air inlet arranged below acombustion chamber. The firing chamber is equipped with a means intendedto initiate the spontaneous combustion of the heterogeneous andpreferably greasy waste. However, such a furnace, specifically suitedfor heterogeneous waste, notably has the drawback of requiring greatcare in handling the waste and of involving uncertain combustionregulation.

Organic waste such as meat flour or palmiped viscera poses difficultcombustion problems because, once dried, the volatile matter content ofthese products is too high to allow direct burning in a conventionalincinerator (grate destruction due to locally high temperatures). In aconventional furnace, the hot zones could be eliminated by using wetwaste (50% water or more), but the geometry of these furnaces is notsuited to allow correct recovery of all the radiation of the flamespresent in the combustion chamber, to warm the waste up and toefficiently eliminate the water contained therein. Spontaneouscombustion is then no longer provided, which sooner or later results ina combustion stop.

SUMMARY OF THE INVENTION

The present invention affords the advantage of allowing to burn wetproducts while maintaining a self-sustaining flame. The problem of hotspots is solved by the presence of water which compensates for the highvolatile matter content of the fuel.

Furthermore, the invention can allow complete automation of anindustrial waste combustion plant.

As will emerge from the description hereafter, the improvement accordingto the invention notably lies in the specific design of the heatingfurnace, at the level of automatic functioning, of emissions and ofenergy recovery.

The present invention thus relates to a device intended for spontaneouscombustion of a fuel comprising organic, vegetable or mineral materials,the device comprising a combustion chamber, at least one fuel injectionmeans, at least one air inlet, hot fumes discharge means. The chambercomprises a cylindrical shell, the discharge means comprise a pipehaving the same axis as the chamber and arranged inside said chamber,and the fuel injection means is arranged substantially tangential tosaid cylindrical shell so that the fuel follows a circular motion aroundsaid pipe in the chamber. The fuel injection means can be placed in thechamber at a distance from the end of the discharge pipe, and the lengthof said pipe in the combustion chamber can be determined to obtain asufficient transit time of the products during combustion before theyare discharged through said pipe.

The device can comprise two fuel injection means that are diametricallyopposite.

The injection means can comprise three concentric tubes intended forinjection of the fuel, of the fuel spraying air and of the combustionair.

The injection means can comprise a spray nozzle consisting of a diskpierced with a port allowing passage of the sprayed fuel jet, the shapeof the disk being such that it can create swirls favouring mixing of theair and of the fuel in the chamber.

The combustion chamber can comprise at least one secondary air inletopening onto the vicinity of the end of the discharge pipe.

The secondary air inlet can be substantially tangential to the shell andso oriented that the secondary air and the fuel move in oppositedirections in the chamber.

There can be two diametrically opposite secondary air inlets.

Chamber preheating means can be arranged in the vicinity of the fuelinjection means.

The preheating means can comprise inlets for hot air coming fromburners.

The chamber can comprise, in the lower part thereof, means allowingrecovery and discharge of the ultimate combustion residue.

The discharge pipe can cooperate with a heat exchanger, for example inorder to provide hot water or steam.

In the device, the combustion air can be supplied by a fan, the fuelspraying air can be provided by a compressor and a pump can supply theinjection means with fuel.

The fuel can be a mixture of water and organic, vegetable or mineralmatter ground into bits whose average size is less than 10 mm andpreferably less than 5 mm.

At least one additive can be added to the fuel in order to stabilize themixture.

An amount of hydrocarbons can also be added in order to raise the meanNCV (net calorific value) of the mixture.

The organic matter of the fuel can come from greasy waste, frompalmipeds for example.

The invention also relates to a method of generating heat energy byimplementing the device described above, wherein the annular volume ofthe combustion chamber is determined to optimize combustion by adjustingthe transit time of the hot gases.

According to the method, the composition and/or spraying of the fuel canbe adjusted so as to have a sufficient amount of fine droplets and/orparticles in order to optimize spontaneous ignition of the fuel.

Without departing from the scope of the present invention, any otherheat and/or steam exchange means can cooperate with the spontaneouscombustion device. The heat produced according to the invention can beused for heating water, steam, or any fluid. Any type of exchanger(tubular, plate exchangers or others) can be used. In general, the heatproduced by the device according to the invention can be used in allindustrial processes, for example thermolysis, or drying of industrialsewage or sludge.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features, details and advantages of the present invention will beclear from reading the description hereafter, given by way of nonlimitative examples, with reference to the accompanying drawingswherein:

FIG. 1 is a longitudinal section of an embodiment of the invention,

FIG. 2 is a longitudinal section of a fuel injection system,

FIG. 3 is a cross-section of the furnace at the level of the fuelinjection means along line 3—3 of FIG. 1,

FIG. 4 is a cross-section of the heating furnace at the level of thesecondary air inlets along line 4—4 of FIG. 1,

FIG. 5 is an overall view of a plant according to the invention.

DETAILED DESCRIPTION

FIG. 1 diagrammatically shows the main elements of the invention. Thespontaneous combustion device comprises a preferably vertical combustionchamber 1. The chamber is cylindrical and comprises a concave bottom orbase equipped with a hopper system 3 for recovery of the burned solidsand discharge through a trap 4. The cylindrical chamber is closed at theupper end thereof by a plate 5 comprising substantially in its axis apipe 6 serving as a stack pipe.

The fuel is injected into chamber 1 through at least one injection means7 arranged substantially tangential to the chamber, so that the fuelfollows a circular motion in the annular space provided between theoutside of pipe 6 and the inside of chamber 1. The details of injectionsystem 7 are described in connection with FIG. 2.

The chamber can comprise other air injection means 8, arranged forexample below fuel injection means 7. These secondary air injectionmeans are arranged substantially tangential to the chamber, but they areso oriented that the air follows a rotating motion in the oppositedirection to that of the fuel injected through means 7.

Other inlets 9, generally arranged above and in the vicinity of the fuelinjection means, allow the combustion chamber to be preheated, either bydirect supply of hot gases coming from an external generator, or by oneor more preheat burners located at inlets 9. These inlets can betangential to the chamber or not. The main purpose of these preheatmeans is to initiate spontaneous combustion of the fuel injected.

The height of the chamber is H, the length of the stack pipe in thechamber is h.

FIG. 2 shows in detail fuel injection means 7.

The fuel can be in the gaseous, liquid or solid phase containingfatal-ashes or not, or a mixture of the three phases. The fuel can be ofthe type described in patent application FR-98/12,751 mentioned herebyway of reference. The fuel is in form of an emulsion that can beeasily transported and sprayed by pressurized air so as to obtaindroplets and/or solid particles whose maximum diameter is less than 10mm and preferably less than 5 mm, and the simultaneous presence of asufficient amount of fine particles or droplets, whose diameter is forexample less than or equal to 25 μm. An amount above about 2% isgenerally sufficient for spontaneous ignition.

FIG. 2 shows injection means 7 comprising a tube 10 secured to the wall11 of combustion chamber 1. Inside this tube 10, two other tubes 12 and13 are placed substantially along the same axis. Tube 12 is ended, onthe combustion chamber side, by a disk or ring 14 provided with a port15 through which the sprayed fuel jet is fed. Inner tube 13 opens ontothe vicinity of port 15, at an optimum distance to allow spraying andefficient mixing of the combustible emulsion injected through theannulus between tubes 13 and 12 and of the pressurized fluid (air)injected through tube 13. Pipe 17 is connected to a pneumaticcompressor, pipe 16 is connected to the fuel pumping means. Primary airthat is injected independently of the fuel in order to control thecombustion of the mixture in chamber 1 circulates between tubes 12 and10.

Disk 14 allows to create sufficient swirls at the level of the fuelinjection means to favour excellent air/fuel mixing.

FIG. 3 is a cross-sectional view of the chamber at the level of a pairof fuel injection nozzles 7. The arrows diagrammatically show the pathof the gases and/or of the particles ignited in chamber 1.

The helical motion imparts a centrifugation phenomenon to the fuel,which allows the heavier (solid or liquid) particles to move towards thewalls of the chamber. The transit time of these particles is thusincreased by this centrifugation phenomenon and it can also be somewhatincreased by a countercurrent secondary air injection. The transit timeof the heavier particles can reach a few minutes, which allows totalcombustion and efficient extraction of the late volatile matter.

FIG. 4 shows the layout of the secondary air inlets in relation to theprimary air inlets and to injection means 7. The direction of rotationof the air is here anticlockwise, whereas the ignited particles and/orgases flow down clockwise in a substantially helical motion in thechamber. Such a layout notably allows to partially stop the helicalmotion with high production of swirls that generates fast mixing of thesecondary air and of the hot fumes, and favours mass and heat transfersby fluidization of the ashes.

The combustion effluents flow out through axial stack pipe 6, generallymade of heat-resisting steel. The function of the stack pipe isfundamental for the operation of the equipment. It generates theradiative stream required for ignition of the fuel, it reduces thevolume of chamber 1 by creating an annular space where combustion takesplace so as to maintain a high and nearly constant velocity of the hotgases around the pipe. The convective stream flowing towards the well ofthe chamber is therefore considerable. The length h of the stack pipe inchamber 1 is determined in relation to the length H of the chamber inorder to compel the hot gases to reach the furnace bottom. Thisretention zone plays a fundamental part. It must be very hot, properlysupplied with oxygen and it must be able to retain the solid matter forseveral minutes in order to allow extraction of the late volatile matterand complete elimination of the carbon contained in the ashes.Combustion of the fuel generates ashes, and hopper 3 is provided toallow easy discharge of this mineral matter.

The radiative emission coefficient of a wall being by nature higher thanthat of gases, the stack pipe allows to transmit to the fuel anappreciable amount of the energy contained in the fumes. The high watercontent of the fuel (30 to 40%) requires a high energy supply in thevicinity of the fuel injection point. The combined effects of theradiation of the walls and of the hot gas circulations produced by disk14 placed at the end of injection tube 12 allow to maintain awell-sustained flame at the outlet of injection means 7.

As shown in FIG. 5, stack pipe 6 can cooperate with a heat-insulated hotwater storage and production tank 20 through which stack pipe 6 runsalong the axis thereof. A heat transfer is thus performed from thecombustion fumes to the water contained in the tank. An air fan 22supplies the primary air inlets 7 and secondary air inlets 8. Anothercompressor, not shown, provides air at a higher pressure for spraying ofthe combustible emulsion. A vessel 25 contains the combustible emulsionprepared by grinding, mixing of greasy waste in the presence of waterand possibly of additives for emulsion stabilization. If the calorificvalue of the waste is not sufficient for optimum operation of the deviceaccording to the invention, the emulsion can be doped with hydrocarbonsor other materials that can raise the mean NCV of the emulsion.

When the spontaneous combustion device according to the invention isthus coupled with a hot water production device, temperature detectors(no reference number) are then provided and cooperate with an automaticcontrol device which can act on fan 22, fuel pump 21 or burners 23 and24 in order to stop or to re-initiate the combustion according to thetemperature of the water in the tank.

Automation of a hot water production device can also comprise an elementsuch as a gas burner of industrial premix burner type, arranged at thebottom of tank 20, independently of combustion chamber 1. This elementcan be used as a safety in case the spontaneous combustion device comesto a standstill, for example when fuel starts running out, or when theheat-capacity rate of the waste is below the required energy supply. Itis then an additional heat supply.

It is clear that the device is not limited to hot water production, andthat its applications as a heat generator can be various and multiple.

The numerous series of tests carried out have allowed to determine theelements that are essential to obtain a good combustion with greasywaste; these elements are as follows:

-   -   using a fuel that can be readily transported between the storage        point and the burner, and possibility of dispersing it in a        gaseous flow in form of droplets and of solid particles (maximum        diameter below 5 mm),    -   combustion system accepting liquid, solid and gaseous products        as well,    -   combustion system accepting solid or liquid particles (or        droplets) that can be fifteen (15) times as big as the largest        particles commonly encountered in combustion of heavy fuel oil        or of pulverized coal,    -   combustion system using a compressed air assistance in order to        produce a sufficient fraction of fine droplets (˜5 to 25 μm)        required for good flame retention,    -   combustion system allowing good mixing of the sprayed fuel and        of the air in order to prevent coking,    -   combustion system with continuous product supply,    -   combustion system of high thermal inertia accepting great        variations in the size of the droplets (or solid material)        injected,    -   combustion system providing both sufficient retention (for a few        minutes) of the products that are the most difficult to bum        (solid products and late volatile matter) and good supply of        this retention zone with a stream of hot gases sufficiently rich        in oxygen (typically 1000° C. and 9% O₂),    -   combustion system allowing proper discharge of the ashes and        with a good corrosion resistance to the fumes,    -   combustion system providing a fumes residence time greater than        or equal to two (2) seconds.

1. A method of generating heat energy, comprising combusting a fuelcomprising organic vegetable or mineral material in a device comprisinga combustion chamber, at least one fuel injection means, chamberpreheating means provided in the vicinity of the fuel injection means,at least one air inlet, and hot fumes discharge means, said chambercomprising a cylindrical shell, said discharge means comprising a pipehaving the same axis as the chamber and arranged inside said chamber,and the fuel injection means being arranged substantially tangential tosaid cylindrical shell so that the fuel follows a circular motion aroundsaid pipe in the chamber, wherein an annular volume of the combustionchamber is determined in order to optimize combustion by adjusting thetransit time of the hot gases.
 2. A method as claimed in claim 1,wherein the composition and/or spraying of the fuel is adjusted so as tohave a sufficient amount of fine droplets and/or particles to optimizespontaneous ignition of the fuel.
 3. A device intended for spontaneouscombustion of a fuel comprising organic, vegetable or mineral materials,said device comprising a combustion chamber, at least one fuel injectionmeans, chamber preheating means provided in the vicinity of the fuelinjection means, at least one air inlet, and hot fumes discharge means,characterized in that said chamber comprises a cylindrical shell, saiddischarge means comprise a pipe having the same axis as the chamber andarranged inside said chamber, and the fuel injection means is arrangedsubstantially tangential to said cylindrical shell so that the fuelfollows a circular motion around said pipe in the chamber and comprisesthree concentric tubes intended for injection of the fuel, of the airallowing said fuel to be sprayed and of the combustion air.
 4. A deviceas claimed in claim 3, wherein the injection means comprises a spraynozzle consisting of a disk pierced with a port allowing passage of thesprayed fuel jet, the shape of the disk being such that it createsswirls favouring air/fuel mixing in the chamber.
 5. A device intendedfor spontaneous combustion of a fuel comprising organic or vegetablematerials, said device comprising a combustion chamber, at least onefuel injection means, chamber preheating means provided in the vicinityof the fuel injection means, at least one air inlet, and hot fumesdischarge means, characterized in that said chamber comprises acylindrical shell, said discharge means comprise a pipe having the sameaxis as the chamber and arranged inside said chamber, and the fuelinjection means is arranged substantially tangential to said cylindricalshell so that the fuel follows a circular motion around said pipe in thechamber, wherein the fuel is a mixture of water and of organic orvegetable matter ground into bits whose average size is less than 10 mm.6. A device as claimed in claim 5, wherein the fuel injection means isarranged at a distance from the end of discharge pipe and the length ofsaid pipe in the combustion chamber is determined to obtain a sufficienttransit time of the products during combustion in the chamber beforethey are discharged through said pipe.
 7. A device as claimed in claim5, wherein two diametrically opposite fuel injection means are provided.8. A device as claimed in claim 5, wherein the chamber comprises atleast one secondary air inlet opening onto the vicinity of the end ofthe discharge pipe.
 9. A device as claimed in claim 8, wherein said airinlet is substantially tangential to said shell and so oriented that thesecondary air in the chamber moves in the opposite direction in relationto the motion of the fuel.
 10. A device as claimed in claim 8, whereinthere are two diametrically opposite air inlets.
 11. A device as claimedin claim 5, wherein said preheating means comprise inlets for hot aircoming from burners.
 12. A device as claimed in claim 5, wherein thechamber comprises, in the lower part thereof, reception and dischargemeans intended for the ultimate combustion residue.
 13. A device asclaimed in claim 5, wherein the discharge pipe cooperates with a heatexchanger in order to provide hot water or steam.
 14. A device asclaimed in claim 5, wherein a fan provides combustion air, a compressorprovides spraying air, a pump supplies the injection means with fuel.15. A device as claimed in claim 5, wherein at least one additive isadded in order to stabilize the combustible mixture.
 16. A device asclaimed in claim 5, wherein an amount of hydrocarbons is added in orderto miss the moan net calorific value of said mixture.
 17. A device asclaimed in claim 5, wherein the organic matter comes from greasy waste.18. A device as claimed in claim wherein the greasy waste compriseswaste from palmipeds.
 19. A device as claimed in claim 19, wherein thefuel is a mixture of water and of organic, vegetable or mineral matterground into bits whose average size is less than 5 mm.
 20. A device asclaimed in claim 19, wherein at least one additive is added in order tostabilize the combustible mixture.
 21. A device as claimed in claim 19,wherein an amount of hydrocarbons is added in order to raise the meannet calorific value of said mixture.
 22. A device as claimed in claim19, wherein the organic matter comes from greasy waste.